Thermoplastic composite structures embedded with at least one load fitting and methods of manufacturing same

ABSTRACT

Manufacturing a thermoplastic composite tubular structure embedded with a first load fitting comprising the steps of braiding a first plurality of inner layers of thermoplastic composite material around a soluble, expandable mandrel. A first load fitting is positioned on the first plurality of inner layers of thermoplastic composite material. A second plurality of outer layers of thermoplastic composite material is braided around the first load fitting and the mandrel so as to form an overbraided mandrel embedded with the first load fitting. The overbraided mandrel is installed into a matched tooling assembly and heated at a specified heating profile in order to consolidate the first plurality of inner layers of thermoplastic composite material and the second plurality of outer layers of thermoplastic composite material with the first load fitting so as to form a thermoplastic composite tubular structure embedded with the first load fitting. A second load fitting may be positioned on the first plurality of inner layers of thermoplastic composite material.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/650,139, filed on Oct. 12, 2012, the entire contents,references and substance of which are hereby incorporated by referenceas if fully set forth below.

FIELD OF THE INVENTION

The present disclosure relates generally to composite structuresembedded with one or more load fittings and methods of manufacturingsame. More particularly, the present disclosure is related tothermoplastic composite tubular structures embedded with at least oneload fitting and methods of manufacturing the same using soluble,expandable tooling.

BACKGROUND

Thermoplastic and fiber-reinforced thermoplastic composite structuresand parts are used in a wide variety of applications, including in themanufacture of aircraft, spacecraft, rotorcraft, watercraft,automobiles, trucks, and other vehicles and structures, due to theirhigh strength-to-weight ratios, corrosion resistance, and otherfavorable properties. In aircraft manufacturing and assembly, suchthermoplastic and fiber-reinforced thermoplastic composite structuresand parts are used in increasing quantities to form the fuselage, wings,tail section, skin panels, and other components.

However, the use of thermoplastic composite materials in the design andmanufacture of tubular cylindrical and non-cylindrical structures, suchas tubes, pipes, ducts, conduits, and elongate hollow components, foruse in aircraft, may present certain difficulties. For example,difficulties can arise due to tooling removal, processing temperature,outer surface dimensional tolerances, fiber alignment, and otherprocessing challenges. Although certain known methods may exist forfabricating tubular cylindrical and non-cylindrical structures, suchknown methods have certain perceived disadvantages. For example, certainknown methods may use only discrete load introduction fittings and partsafter overbraiding the fabricated tubular cylindrical andnon-cylindrical structures. Consequently, such known methods may requirea failsafe redundant structure, which may include a primary weld of thefabricated structures. Aside from this primary weld, a wrap of thebraided fibers may further be required to manufacture the fabricatedtubular cylindrical and non-cylindrical structures with one or more loadfittings or load introduction points.

Therefore, manufacturing options for such known methods may result inincreased manufacturing time, and in turn, increased manufacturingcosts. Further, the failsafe redundant structure typically may result inincreased weight of the aircraft, which, in turn, may result inincreased fuel costs during aircraft flight.

Accordingly, there is a need for improved thermoplastic compositetubular structures that can be embedded with one or more load fittings.There is also a need for improved methods for manufacturing suchthermoplastic composite tubular structures embedded with load fittingsthat provide advantages over known structures and methods.

SUMMARY

According to an exemplary arrangement, embodiments of the improvedthermoplastic composite tubular structures embedded with at least oneload fitting and improved methods for manufacturing such thermoplasticcomposite tubular structures embedded with at least one load fitting ispresented.

In one arrangement, a method of manufacturing a thermoplastic compositetubular structure embedded with a first load fitting comprises the stepof braiding a first plurality of inner layers of thermoplastic compositematerial around a mandrel, the mandrel comprising a soluble, expandablematerial and comprising a mandrel cross-section defining a first closedgeometric shape. The method comprises the step of placing a first loadfitting on the first plurality of inner layers of thermoplasticcomposite material and braiding a second plurality of outer layers ofthermoplastic composite material around the first load fitting and themandrel so as to form an overbraided mandrel embedded with the firstload fitting.

In another arrangement, the method further comprises the step ofinstalling the overbraided mandrel embedded with the first load fittinginto a matched tooling assembly. The method may also include the step ofheating in a heating apparatus the matched tooling assembly with theinstalled overbraided mandrel embedded with the first load fittingmember at a specified heating profile in order to consolidate the firstplurality of inner layers of thermoplastic composite material and thesecond plurality of outer layers of thermoplastic composite materialwith the first load fitting so as to form a thermoplastic compositetubular structure embedded with the first load fitting. In yet anotherarrangement, the heating apparatus is selected from the group consistingof a convection oven, an induction oven, an autoclave, an inductionheated matched tooling assembly, and an integrally heated toolingassembly. In addition, the specified heating profile comprises a heatingtemperature in a range of from about 150 degrees Fahrenheit to about 800degrees Fahrenheit and a heating time in a range of from about 5 minutesto about 120 minutes.

In one arrangement, upon heating in the heating apparatus, theexpandable material of the mandrel expands and exerts pressure on theplurality of inner and outer layers of thermoplastic composite materialagainst the matched tooling assembly causing consolidation of theplurality of inner and outer layers of thermoplastic composite materialwith the at least one load fitting.

In one arrangement, the method further comprises the steps of coolingthe matched tooling assembly containing the formed thermoplasticcomposite tubular structure embedded with the first load fitting at aspecified cooling profile, and removing the formed thermoplasticcomposite tubular structure embedded with the first load fitting fromthe matched tooling assembly.

In one arrangement, the method may further comprise the step ofsolubilizing the mandrel to remove the mandrel from the formedthermoplastic composite tubular structure embedded with the first loadfitting.

In yet another arrangement, the overbraided mandrel embedded with thefirst load fitting comprises an overbraided mandrel cross-sectiondefining a second closed geometric shape, the second closed geometricshape corresponding to the first closed geometric shape of the mandrelcross-section.

In yet another arrangement, the method includes the steps of braidingthe first plurality of inner layers of thermoplastic composite materialaround the mandrel to define a first inner layer depth and braiding thesecond plurality of outer layers of thermoplastic composite materialaround the first load fitting and the mandrel to define a second outerlayer depth so as to form an overbraided mandrel embedded with the firstload fitting. The first inner layer depth of the first plurality ofinner layers of thermoplastic composite material may be the same or maybe different than the second outer layer depth of the second pluralityof outer layers of thermoplastic composite material.

In yet another arrangement, the method further comprises the steps ofplacing a second load fitting on the first plurality of inner layers ofthermoplastic composite material and braiding the second plurality ofouter layers of thermoplastic composite material around the first loadfitting, the second load fitting, and the mandrel so as to form anoverbraided mandrel embedded with the first and second load fitting.

In one arrangement, the soluble, expandable material of the mandrel isselected from the group consisting of one or more of ceramic, sand, apolymer binder, a soluble organic binder, a soluble inorganic binder,sodium silicate, graphite, one or more additives, and one or morepreservatives.

In one arrangement, the first closed geometric shape is selected fromthe group consisting of a circle, a semi-circle, a rectangle, an oval,an ellipse, a parallelogram, a trapezoid, a rhombus, a curvilineartriangle, a crescent, a quadrilateral, a quatrefoil, and a polygoncomprising a triangle, a square, a pentagon, a hexagon, a heptagon, anoctagon, a nonagon, a decagon, a hendecagon, and a dodecagon.

In one arrangement, the plurality of inner layers of thermoplasticcomposite material are materials selected from the group consisting ofcarbon fiber composite material; carbon fiber reinforced polymermaterial including carbon fiber reinforced polyphenylene sulfide (PPS),carbon fiber reinforced polyetheretherketone (PEEK), carbon fiberreinforced polyetherketoneketone (PEKK), and carbon fiber reinforcedpolyetherimide (PEI); and nylon.

In yet another arrangement, the plurality of inner layers ofthermoplastic composite material are in a form selected from the groupconsisting of a continuous slit tape thermoplastic composite material, aprepreg unidirectional tape, a prepreg fabric, a commingled fibermaterial, and a quasi-isotropic or anisotropic continuous fiberthermoplastic composite material.

In yet another arrangement, the matched tooling assembly comprises ametallic clamshell tooling assembly.

In yet another arrangement, a specified cooling profile comprises atemperature below a glass transition temperature of the plurality ofinner and outer layers of thermoplastic composite material forming theoverbraided mandrel embedded with the at least one load fitting.

In yet another arrangement, a step of solubilizing the mandrel furthercomprises solubilizing the mandrel with water or a water-based solutionto permanently remove the mandrel from the formed thermoplasticcomposite tubular structure embedded with the first load fitting.

In yet another arrangement, a step of braiding the plurality of outerlayers of thermoplastic composite material around the first load fittingand the mandrel further comprises the step of tailoring a depth of thefirst load introduction member to a type and magnitude of a load beingintroduced to the thermoplastic composite tubular structure embeddedwith the first load fitting.

In yet another arrangement, the first plurality of inner layerscomprises a first braided configuration and the second plurality ofouter layers comprises a second braided configuration. The first braidedconfiguration may be the same or may be different than the secondbraided configuration.

In yet another arrangement, a thermoplastic composite tubular structureembedded with a first load fitting, comprises a first plurality of innerlayers of thermoplastic composite material braided around a mandrel, themandrel comprising a soluble, expandable material and comprising amandrel cross-section defining a first closed geometric shape. A firstload fitting is placed on the first plurality of inner layers ofthermoplastic composite material and a second plurality of outer layersof thermoplastic composite material braided around the first loadfitting and the mandrel so as to form an overbraided mandrel embeddedwith the first load fitting. The soluble, expandable material of themandrel may be selected from the group consisting of one or more ofceramic, sand, a polymer binder, a soluble organic binder, a solubleinorganic binder, sodium silicate, graphite, one or more additives, andone or more preservatives. Additionally, the first closed geometricshape may be selected from the group consisting of a circle, asemi-circle, a rectangle, an oval, an ellipse, a parallelogram, atrapezoid, a rhombus, a curvilinear triangle, a crescent, aquadrilateral, a quatrefoil, and a polygon comprising a triangle, asquare, a pentagon, a hexagon, a heptagon, an octagon, a nonagon, adecagon, a hendecagon, and a dodecagon.

In another alternative arrangement, the plurality of inner layers ofthermoplastic composite material are materials selected from the groupconsisting of carbon fiber composite material; carbon fiber reinforcedpolymer material including carbon fiber reinforced polyphenylene sulfide(PPS), carbon fiber reinforced polyetheretherketone (PEEK), carbon fiberreinforced polyetherketoneketone (PEKK), and carbon fiber reinforcedpolyetherimide (PEI); and nylon. Additionally, the plurality of innerlayers of thermoplastic composite material may be in a form selectedfrom the group consisting of a continuous slit tape thermoplasticcomposite material, a prepreg unidirectional tape, a prepreg fabric, acommingled fiber material, and a quasi-isotropic or anisotropiccontinuous fiber thermoplastic composite material.

In yet another arrangement, the plurality of outer layers ofthermoplastic composite material braided around the first load fittingand the mandrel may be tailored to a depth relating to a type andmagnitude of a load being introduced to the thermoplastic compositetubular structure embedded with the first load fitting.

In yet another arrangement, the thermoplastic composite tubularstructure may comprise a second load fitting. This second load fittingmay be placed on the first plurality of inner layers of thermoplasticcomposite material.

The features, functions, and advantages can be achieved independently invarious embodiments of the present disclosure or may be combined in yetother embodiments in which further details can be seen with reference tothe following description and drawings.

BRIEF DESCRIPTION OF THE FIGURES

The novel features believed characteristic of the illustrativeembodiments are set forth in the appended claims. The illustrativeembodiments, however, as well as a preferred mode of use, furtherobjectives and descriptions thereof, will best be understood byreference to the following detailed description of an illustrativeembodiment of the present disclosure when read in conjunction with theaccompanying drawings, wherein:

FIG. 1 is an illustration of a perspective view of an aircraft which mayincorporate one or more thermoplastic composite tubular structuresfabricated by one of the embodiments of a method of the disclosure;

FIG. 2 is an illustration of a flow diagram of an embodiment of anaircraft manufacturing and service method of the disclosure;

FIG. 3 is an illustration of a functional block diagram of an aircraft;

FIG. 4A is an illustration of a perspective view of one of theembodiments of a mandrel that may be used in method embodiments of thedisclosure;

FIG. 4B is an illustration of a cross-sectional view taken along lines4B-4B of FIG. 4A;

FIG. 4C is an illustration of a perspective view of another one of theembodiments of a mandrel that may be used in method embodiments of thedisclosure;

FIG. 4D is an illustration of a cross-sectional view taken along lines4D-4D of FIG. 4C;

FIG. 4E is an illustration of a cross-sectional view taken along lines4E-4E of FIG. 4C;

FIG. 5 is an illustration of a schematic view of a braiding apparatusoverbraiding one of the embodiments of a mandrel with a first pluralityof inner layers of thermoplastic composite material that may be used inmethod embodiments of the disclosure;

FIG. 6 is an illustration of one arrangement of a load fitting that canbe positioned on the first plurality of inner layers of thermoplasticcomposite material illustrated in FIG. 5;

FIG. 7 is an illustration of positioning at least one load fitting thatmay be used in method embodiments of the disclosure;

FIG. 8A is an illustration of an overbraided mandrel embedded with atleast one load fitting that may be used in method embodiments of thedisclosure;

FIG. 8B is cross-sectional illustration of the overbraided mandrelembedded with the at least one load fitting illustrated in FIG. 8A;

FIG. 9A is an illustration of a close-up top view of an overbraidedmandrel having a first braided configuration that may be used in methodembodiments of the disclosure;

FIG. 9B is an illustration of a close-up top view of an overbraidedmandrel having an alternative braided configuration that may be used inmethod embodiments of the disclosure;

FIGS. 10A-E are illustrations of various process steps of installing anoverbraided mandrel embedded with at least one load fitting into amatched tooling assembly that may be used in method embodiments of thedisclosure;

FIG. 11 is an illustration of a cut-away perspective view of anoverbraided mandrel embedded with at least one load fitting installed ina matched tooling assembly being heated in a heating apparatus that maybe used in method embodiments of the disclosure;

FIG. 12 is an illustration of a perspective view of a mandrel embeddedwith at least one load fitting being washed out of the formedthermoplastic composite tubular structure in a mandrel removal apparatusthat may be used in method embodiments of the disclosure;

FIG. 13 is an illustration of a flow diagram illustrating one of theembodiments of a method of the disclosure;

FIGS. 14A-B are an illustration of a flow diagram illustrating anotherone of the embodiments of a method of the disclosure; and,

FIGS. 15A-B are an illustration of a flow diagram illustrating anotherone of the embodiments of a method of the disclosure.

DETAILED DESCRIPTION

Disclosed embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which some, but not all ofthe disclosed embodiments are shown. Indeed, several differentembodiments may be provided and should not be construed as limited tothe embodiments set forth herein. Rather, these embodiments are providedso that this disclosure will be thorough and complete and will fullyconvey the scope of the disclosure to those skilled in the art.

FIG. 1 is an illustration of a perspective view of an aircraft 10 thatmay incorporate one or more thermoplastic composite tubular structuresembedded with at least one load fitting 26 manufactured by one of theembodiments of a method 200 (see FIG. 13), a method 250 (see FIGS.14A-B), or a method 300 (see FIGS. 15A-B) of the disclosure. As shown inFIG. 1, the aircraft 10 comprises a fuselage 12, a nose 14, a cockpit16, wings 18 operatively coupled to the fuselage 12, one or morepropulsion units 20, a tail vertical stabilizer 22, and one or more tailhorizontal stabilizers 24. Although the aircraft 10 shown in FIG. 1 isgenerally representative of a commercial passenger aircraft, the one ormore thermoplastic composite tubular structures embedded with at leastone load fitting 26, as disclosed herein, may also be employed in othertypes of aircraft or air vehicles. More specifically, the teachings ofthe disclosed embodiments may be applied to other passenger aircraft,cargo aircraft, military aircraft, rotorcraft, and other types ofaircraft or aerial vehicles, as well as aerospace vehicles, satellites,space launch vehicles, rockets, and other aerospace vehicles. It mayalso be appreciated that embodiments of structures and methods inaccordance with the disclosure may be utilized in other transportvehicles, such as boats and other watercraft, trains, automobiles,trucks, buses, or other suitable transport vehicles formed from orutilizing thermoplastic composite tubular structures or parts.

Embodiments of the disclosure may find use in a variety of potentialapplications, particularly in the transportation industry, including forexample, aerospace, marine, automotive applications and otherapplication where thermoplastic composite tubular structures may beused. Therefore, referring now to FIGS. 2 and 3, embodiments of thedisclosure may be used in the context of an aircraft manufacturing andservice method 30 as shown in FIG. 2 and an aircraft 50 as shown in FIG.3. Aircraft applications of the disclosed embodiments may include, forexample, without limitation, the design and fabrication of thermoplasticcomposite tubular structures comprising at least one embedded loadfitting. During pre-production, exemplary method 30 may includespecification and design 32 of the aircraft 50 and material procurement34. As just one example, for the specification and design of theaircraft related thermoplastic composite tubular structures, the typeand geometrical properties of the thermoplastic composite materialmaking up the first plurality of inner layers and the second pluralityof outer layers of the resultant tubular structures may be determined atthis step.

As another example, during this specification and design step, in oneparticular thermoplastic composite tubular structure arrangement, thefirst plurality of inner thermoplastic composite material 96 a (see FIG.4A), the second plurality of inner thermoplastic composite material 96b, and the load fitting 103 are preferably sized to together carry anultimate load. In addition, the resulting formed thermoplastic compositetube is preferably designed and therefore sized to carry a limit load.Limit loads are defined as the maximum loads expected in service. Forexample, Federal Aviation Administration (FAA) Federal AviationRegulation (FAR) Part 25 specifies that there be no permanentdeformation of the structure at limit load. Ultimate loads are definedas the limit loads times a safety factor. FAA FAR Part 25 specifies thesafety factor as 1.5. For some research or military aircraft the safetyfactor may be as low as 1.20.

In addition, during this specification and design step 32 of method 30,the type and composition of the load fitting to be used in a particularthermoplastic composite tubular structure loading application that willbe embedded between the first and second layers of thermoplasticmaterials may be selected. As just another example, the number of loadfittings and the orientation and alignment of the load fitting(s) mayalso be determined during this process step 32. As just one example, theresultant thermoplastic composite tube comprises at least one loadfitting that is consolidated between the first plurality of inner layersof thermoplastic material 96 a and the second plurality of outer layersof thermoplastic material 96 b. In one arrangement, the inner and outerlayers of the thermoplastic tube are configured to provide reinforcementand impact damage resistance to the load fitting 103 that comprises amain body 155 and a male clevis portion 170 (see e.g., FIG. 6) in orderto prevent a loss in structural loading capability.

During production, component and subassembly manufacturing 36 and systemintegration 38 of the aircraft 50 takes place. As will be explained ingreater detail, FIGS. 12, 13, 14A-B, illustrate three type process stepsfor fabricating thermoplastic composite tubule structures with at leastone load fitting in accordance with the present disclosure. After such acomponent and subassembly manufacturing step, the aircraft 50 may gothrough certification and delivery 40 in order to be placed in service42. While in service by a customer, the aircraft 50 is scheduled forroutine maintenance and service 44, which may also include modification,reconfiguration, refurbishment, and so on.

Each of the process steps of method 50 may be performed or carried outby a system integrator, a third party, and/or an operator (e.g., acustomer). For the purposes of this description, a system integrator mayinclude without limitation any number of aircraft manufacturers andmajor-system subcontractors; a third party may include withoutlimitation any number of vendors, subcontractors, and suppliers; and anoperator may be an airline, leasing company, military entity, serviceorganization, and so on.

As shown in FIG. 3, the aircraft 50 produced by exemplary method 30 mayinclude an airframe 52 with a plurality of high-level systems 54 and aninterior 56. Examples of high-level systems 54 may include one or moreof a propulsion system 58, an electrical system 60, a hydraulic system62, and an environmental system 64. Any number of other systems may beincluded. Although an aerospace example is shown, the principles of thedisclosure may be applied to other industries, such as the marine andautomotive industries.

Systems and methods embodied herein may be employed during any one ormore of the stages of the production and service method 30. For example,components or subassemblies corresponding to production process may befabricated or manufactured in a manner similar to components orsubassemblies produced while the aircraft 50 is in service. Also, one ormore apparatus embodiments, method embodiments, or a combination thereofmay be utilized during the production stages 32 and 34, for example, bysubstantially expediting assembly of or reducing the cost of an aircraft50. Similarly, one or more of apparatus embodiments, method embodiments,or a combination thereof may be utilized while the aircraft 50 is inservice, for example and without limitation, to maintenance and service44.

In one embodiment of the disclosure, there is provided a method 200 ofmanufacturing a thermoplastic composite tubular structure embedded withat least one load fitting, such as the thermoplastic composite tubularstructures 26 illustrated in FIG. 1. For example, FIG. 13 is anillustration of a flow diagram illustrating a method 200 of thedisclosure. For purposes of this patent disclosure, the term “tubularstructure” means a structure having a cylindrical or non-cylindricalshape, having a linear or non-linear shape in a lengthwise direction,and having a cross-section defining a closed geometric shape (discussedin detail below). The tubular structure may or may not be hollow or maybe partially hollow.

As shown in FIG. 13, the method 200 comprises step 202 of providing amandrel 70 or tooling (see FIG. 4A) comprised of a soluble, expandablematerial 72 (see FIGS. 4A, 4C). For example, FIG. 4A is an illustrationof a perspective view of one of the embodiments of the mandrel 70, suchas in the form of mandrel 70 a. Such a mandrel 70 a may be used in themethod 200 (as well as in method 250 (see FIGS. 14A-B) and method 300(see FIGS. 15A-B)), of the disclosure. FIG. 4C is an illustration of aperspective view of another one of the embodiments of a mandrel 70 bthat may be used in the method 200 of the disclosure. The mandrel 70 maytherefore, for example, be in the form of mandrel 70 a (see FIG. 4A) ormandrel 70 b (see FIG. 4C), or another suitable mandrel form.

The mandrel 70 preferably comprises one or more soluble, expandablematerials. Such materials may consist of ceramic, sand, a polymerbinder, a soluble organic binder, a soluble inorganic binder, sodiumsilicate, graphite, one or more additives, and one or morepreservatives, or another suitable soluble, expandable material.Preferably, the mandrel material is a high expansion material.Embodiments of the mandrel or mandrel materials that may be used in thepresently disclosed methods include the mandrel and mandrel materialsdisclosed in U.S. patent application Ser. No. 13/650,139 entitled“Thermoplastic Composite Tubular Structures using Soluble High ExpansionTooling Materials,” herein entirely incorporated by reference and towhich the reader is directed for further information.

Preferably, the mandrel 70 comprises a mandrel cross-section 74 defininga first closed geometric shape 76. For example, FIG. 4B is anillustration of a cross-sectional view taken along lines 4B-4B of themandrel 70 illustrated in FIG. 4A. As shown in FIG. 4A, the mandrel 70,such as in the form of mandrel 70 a, may comprise a cylindrical ortubular mandrel 78 having a linear shape 80 and a generally smoothexternal surface 98. As illustrated in FIG. 4B, the tubular mandrel 78has the mandrel cross-section 74, such as in the form of a mandrelcross-section 74 a, defining the first closed geometric shape 76, suchas a first closed geometric shape 76 a, in the shape of a circle 82.

As shown in FIG. 4C, the mandrel 70 b comprises a non-cylindricalmandrel 84 having a non-linear shape 86. FIG. 4D is an illustration of across-sectional view taken along lines 4D-4D of FIG. 4C. Thenon-cylindrical mandrel 84 has the mandrel cross-section 74, such as inthe form of cross-section 74 b (see FIG. 4D), defining the first closedgeometric shape 76 at a first end 88 (see FIG. 4C), such as a firstclosed geometric shape 76 b (see FIG. 4D), in the shape of a square 90(see FIG. 4D). FIG. 4E is an illustration of a cross-sectional viewtaken along lines 4E-4E of FIG. 4C. As can be seen from FIG. 4E, thenon-cylindrical mandrel 84 has the mandrel cross-section 74, such as inthe form of cross-section 74 c, defining the first closed geometricshape 76 at a second end 92 (see FIG. 4C), such as a first closedgeometric shape 76 c, in the shape of a rectangle 94 (see FIG. 4E).

In addition to the shapes of the circle 82 and the rectangle 94 asillustrated in FIGS. 4B and 4E, the first closed geometric shape 76 mayfurther include such shapes as a semi-circle, an oval, an ellipse, aparallelogram, a trapezoid, a rhombus, a curvilinear triangle, acrescent, a quadrilateral, a quatrefoil, and polygon shapes, in additionto the square 90 (see FIG. 4D), comprising a triangle, a pentagon, ahexagon, a heptagon, an octagon, a nonagon, a decagon, a hendecagon, adodecagon, or another suitable closed geometric shape.

Returning to FIG. 13, the method 200 further comprises an initial step204 of braiding a first plurality of inner layers of thermoplasticcomposite material 96 a around the mandrel 70 over an exterior surface98 (see FIG. 5) of the mandrel 70, such as in the form of the tubularmandrel 78. In one preferred arrangement, and as will be described ingreater detail herein, the method 200 may comprise the step of braidingthe first plurality of inner layers of thermoplastic composite materialaround the external surface of the mandrel so as to define a first innerlayer depth. Preferably, this first inner layer depth may be determinedduring the specification and design step 32 as described with respect toFIG. 1. In one arrangement, this first inner layer depth may be definedin part by the loading characteristics of the subsequently manufacturedthermoplastic composite tubular structure.

Returning to the method 200 illustrated in FIG. 13, step 206 illustratesthe step of positioning at least one load fitting 103 on the firstplurality of inner layers of thermoplastic composite material 96 a (seeFIG. 7). During this step, or perhaps after subsequent braiding steps, asecond load fitting may be positioned on the partially braided mandrel70. Then, the method continues to step 208 which includes the step ofbraiding a second plurality of outer layers of thermoplastic compositematerial 96 b around the mandrel 70 and the at least one load fitting103 so as to form an overbraided mandrel embedded with the at least oneload fitting 100 (see FIG. 8A).

In one preferred arrangement, braiding of the second plurality of outerlayers of thermoplastic composite material around the at least one loadfitting defines a second outer layer depth of composite material.Preferably, this second outer layer depth may be determined during thespecification and design step 32 as described with respect to FIG. 1. Inone arrangement, this second outer layer depth may be defined in part bythe loading characteristics of the subsequently manufacturedthermoplastic composite structure.

The use of the first plurality of inner layers of thermoplasticcomposite material 96 a and the second plurality of outer layers ofthermoplastic composite material 96 b allows for preferredconfigurations or designs of the thermoplastic composite tubularstructures embedded with at least one load fitting 26 to be fabricateddue to its ability to form structures in more complicated shapes.Additionally, the use of the first plurality of inner layers ofthermoplastic composite material 96 a and second plurality of outerlayers of thermoplastic composite material 96 b may allow an axialposition or axial depth of a load fitting within the thermoplasticcomposite tubular structure to be varied or tailored to the type andmagnitude of the load being introduced to the thermoplastic compositetubular structures.

For example, FIG. 8B provides a cross sectional illustration of thebraided mandrel 100 illustrated in FIG. 8A. As illustrated in FIG. 8B,the first plurality of inner layers of thermoplastic composite material96 a has been braided around the mandrel 78 where the first plurality ofinner layers define a first inner layer depth D_(Inner) 92. As those ofordinary skill in the art will recognize, if more layers ofthermoplastic composite material 96 a are braided onto the outer surfaceof the mandrel 78, the first inner layer depth D_(Inner) 92 wouldincrease. As also illustrated, the load fitting 103 is provided in aseated position on top of this first inner layer and is thereforeprovided at a depth D_(Inner) 92 from the outer surface 98 of themandrel 78. In this illustrated arrangement, a curvature of the bottomsurface of the load fitting 103 generally corresponds with a radius ofcurvature of the first plurality of inner layers 96 a.

In a subsequent process step, the second plurality of outer layers ofthermoplastic composite material 96 b is braided around the nowpositioned first load fitting 103, the mandrel 78, and the firstplurality of inner layers 96 a. The amount of the second plurality ofouter layers 96 b defines a second outer layer depth D_(Outer) 93 thatnow forms an overbraided mandrel 100. As illustrated, the first innerlayer depth of the first plurality of inner layers of thermoplasticcomposite material D_(Inner) 92 is different than the second outer layerdepth of the second plurality of outer layers of thermoplastic compositematerial D_(Outer) 93. However, as those of skill in the art willrecognize, different overbraided mandrel configurations comprisingalternative first inner layer depth and second outer layer depthconfigurations may also be utilized.

In a preferred arrangement, the inner and outer thermoplastic materials96 a, 96 b, respectively, may comprise slit tape thermoplasticmaterials. The utilization of slit tape thermoplastic material for theinner and outer thermoplastic materials may provide certain advantages,such as decreased tape crossover and kinking. Specifically, the firstplurality of inner layers of thermoplastic composite material 96 apreferably consists of a carbon fiber composite material; carbon fiberreinforced polymer material including carbon fiber reinforcedpolypheylene sulfide (PPS), carbon fiber reinforced polyetheretherketone(PEEK), carbon fiber reinforced polyetherketoneketone (PEKK), and carbonfiber reinforced polyetherimide (PEI); nylon, or another suitablethermoplastic composite material. One advantage of using suchthermoplastic materials is that they allow for co-consolidation of theinner and outer thermoplastic materials to the load fitting 103. Inaddition, such the thermoplastic materials for potential welding ofsupport or systems brackets to the resulting thermoplastic compositetubular structure 132. (see, FIG. 12).

The plurality of inner layers of thermoplastic composite material 96 aand plurality of outer layers of thermoplastic composite material 96 bare preferably in a form consisting of a continuous slit tapethermoplastic composite material, a prepreg unidirectional tape, aprepreg fabric, a commingled fiber material, a quasi-isotropic oranisotropic continuous fiber thermoplastic composite material, oranother suitable continuous fiber thermoplastic composite material.

In one arrangement, the second plurality of outer layers ofthermoplastic composite material 96 b may comprise the same type ofmaterial as the first plurality of inner layers of thermoplasticcomposite material 96 a. Alternatively, the second plurality of outerlayers of thermoplastic composite material 96 b may comprise a differentmaterial as the first plurality of inner layers 96 a.

Preferably, the first plurality of inner layers of thermoplasticcomposite material 96 a comprises a form of prepreg unidirectional tape106, such as a narrow width of % inch wide, ¼ inch wide, or anothersuitably narrow width tape. The commingled fiber material may comprisedry fibers with a thermoplastic resin powder embedded in the dry fibers.In one preferred arrangement, the second plurality of outer layers ofthermoplastic composite material 96 b may comprise a similar width or adifferent width as the first plurality of inner layers of thermoplasticcomposite material 96 a.

The plurality of inner layers of thermoplastic composite material 96 amay be wound and/or braided around the mandrel in a zero (0) degreedirection and also wound or braided in a bias direction. When theplurality of inner layers of thermoplastic composite material 96 a andplurality of outer layers of thermoplastic composite material 96 b arewound or braided in a bias direction, the commingled fiber material maybe used so that when the plurality of inner layers of thermoplasticcomposite material 96 a and plurality of outer layers of thermoplasticcomposite material 96 b are heated and consolidated, the embedded resinpowder fills the dry fibers and melts to result in the consolidatedthermoplastic composite tubular structure embedded with at least oneload introduction point 26. In one preferred arrangement, the secondplurality of outer layers of thermoplastic composite material 96 b maybe wound in a similar or perhaps in a different manner than the firstplurality of inner layers of the thermoplastic composite material 96 a.

For purposes of this patent disclosure, “quasi-isotropic continuousfiber thermoplastic composite material” means a laminate thatapproximates isotropy by orientation of tows in several or moredirections in-plane. For example, a quasi-isotropic part may haverandomly oriented fibers in all directions or may have fibers orientedsuch that equal strength is developed all around the plane of the part.In general, a quasi-isotropic laminate made from a prepreg fabric orwoven fabric may have tows oriented at 0° (zero degrees), 90°, +45°, and−45°, with at least 12.5% of the tows in each of these four directions.Quasi-isotropic properties may also be obtained with braidedunidirectional (0 degree) and 60 degree bias oriented tows. For purposesof this disclosure, “anisotropic continuous fiber thermoplasticcomposite material” means the composite material's directionaldependence of a physical property and can be a difference, when measuredalong different axes, in a material's physical or mechanical properties(absorbance, refractive index, conductivity, tensile strength, etc.).Anisotropic may also be referred to as “unidirectional”.

Returning to the method 200 in FIG. 13, as well as method 250illustrated in FIGS. 14A-B and method 300 illustrated in FIGS. 15A-B,method 200 provides for fabricating and configuration of highly loadedquasi-isotropic or highly loaded anisotropic (unidirectional)thermoplastic composite continuous fiber tubular structures embeddedwith at least one load fitting with the use of soluble, expandable (highexpansion) mandrels or tooling materials.

FIG. 5 is an illustration of a schematic top view of a braidingapparatus 102 that may be used for overbraiding one of the embodimentsof a mandrel 70 with a first plurality of inner layers of thermoplasticcomposite material 96 a and that may be used in method embodiments ofthe disclosure. As shown in FIG. 5, the overbraiding of the mandrel 70is preferably accomplished by using the braiding apparatus 102 havingone or more braiding bobbins or tubes 104 for dispensing and braidingthe plurality of inner layers of thermoplastic composite material 96 aover the mandrel 70. In one preferred arrangement, the first pluralityof inner layers comprise a first braided configuration defining a firstinner layer depth D_(Inner) 92 of the thermoplastic composite material96 a. A braiding apparatus or machine known in the art may be used tooverbraid the mandrel 70.

After the first braided configuration of the thermoplastic compositematerial 96 a has been braided along the outer surface 98 of the mandrel70 so as to define the first inner layer depth, a load fitting may beplaced on the mandrel. As just one example, such a load fitting maycomprise a saddle or hyperbolic paraboloid shaped load fitting.

For example, FIG. 6 illustrates a perspective view of one arrangement ofa load fitting 150 that may be used with the partially overbraidedmandrel 70 illustrated in FIG. 5. In this load fitting arrangement, theload fitting 150 may take the form of a saddle shaped load fitting. Asillustrated, the load fitting 150 comprises a main body 155 generallycomprising an oval, elongated shape and comprising an upper surface 160and a lower surface 165. The lower surface 160 comprises a bearingsurface for residing on top the first plurality thermoplastic compositematerial 96 a. The upper surface 160 of the main body 155 of the loadfitting 150 comprises a male clevis 170. This male clevis 170 isconfigured to extend from a central portion 158 of the main body 155. Inthis illustrated arrangement, the male clevis 170 defines an opening175. Such an opening 175 may be used to receive a bolt or other likeattachment element. In one preferred arrangement, the main body 155defines a radius of curvature generally equivalent to an outer curvatureof the mandrel 70 and the first plurality of inner layers ofthermoplastic composite materials 96 a illustrated in FIG. 5.

The composition and geometrical shape of the load fitting 150illustrated in FIG. 6 may be defined during the specification and designstep 32 of the method 30 illustrated in FIG. 2. For example, during thisspecification and design step 32, it may be determined that the loadfitting 150 comprise a metallic material such as titanium, carboncomposite, aluminum, stainless steel, or other suitable material. In onepreferred arrangement, the load fitting 150 comprises a unitary titaniumfitting. Prior to placing the load fitting 150 on the mandrel comprisingthe first plurality of inner layers of thermoplastic, the bottom and topsurfaces or the load bearing surface of the load fitting 150 may beprepared or treated. Such load bearing surface preparation may includethe steps of cleaning and mechanical pretreatment, application of anadhesion promoter, or application of a polyimide based primer.

As shown in FIG. 7, at least one load fitting 103 (such as the saddleshaped load fitting 150 illustrated in FIG. 6) is positioned on theplurality of inner layers of thermoplastic composite material 96 a whichhave been braided along the mandrel outer surface. Where more than oneload fitting 103 is positioned along the inner layers of compositematerial 96 a, the process may also require that these fittings 103 (andparticularly the male clevis of these fittings) are aligned with oneanother over the length of the braided structure. Alternatively, wheremore than one load fitting is utilized, these fittings (and thereforethe male clevis of these fittings) may be offset from one another. Inone preferred arrangement, the second plurality of inner layer ofcomposite materials comprise a second braided configuration defining asecond depth of the thermoplastic composite material 96 b.

Overbraiding of the load fitting 103 and the inner layers of thecomposite material 96 a is preferably accomplished by using the samebraiding apparatus 102 having one or more braiding bobbins or tubes 104(see FIG. 5) for dispensing and braiding the plurality of outer layersof thermoplastic composite material 96 b over the mandrel 70 and atleast one load fitting 103. This overbraiding forms an over braidedmandrel embedded with at least one saddle-based load fitting 100 asillustrated in FIG. 8A. Preferably, the known braiding apparatus ormachine has the capability of accommodating changes to the thermoplasticcomposite material's thickness, gauge, bias angle along the length,cross-sectional shape, cross-sectional angular path along the length,curve, shape of drop, and number of tows. Preferably, the overbraidingof the mandrel 70 and the load fitting 103 is carried out at ambienttemperature.

The overbraiding process preferably provides for improved damagetolerance and improved fracture toughness properties of the plurality ofinner layers of thermoplastic composite material 96 a and plurality ofouter layers of thermoplastic composite material 96 b due to the overand under construction of the overbraiding process. In one embodiment,the overbraided mandrel embedded with the load fitting 100 asillustrated in FIG. 8A may comprise a plurality of inner layers ofthermoplastic composite material 96 a and plurality of outer layers ofthermoplastic composite material 96 b with a bias tow only overbraid 101a.

As discussed above, in one preferred arrangement, the first plurality ofinner layers may comprise a first braided configuration and this firstbraided configuration defines a first depth of the thermoplasticcomposite material 96 a. Similarly, the second plurality of inner layersmay comprise a second braided configuration defining a second depth ofthe thermoplastic composite material 96 b. The first braidedconfiguration may be the same as or may be different from the secondbraided configuration.

For example, FIG. 9A illustrates a braided configuration 113 comprisinga biaxial braided configuration 114. FIG. 9B illustrates a braidedconfiguration 116 that is different than the biaxial braidedconfiguration 114 illustrated in FIG. 9A. Specifically, this alternativebraided configuration 116 illustrated in FIG. 9B comprises a triaxialbraided configuration 117. Preferably, in one arrangement, the firstbraided configuration of the inner layers of the thermoplastic compositematerial 96 a and the second braided configuration of the outer layersof the thermoplastic composite material 96 b both comprise either abiaxial braided configuration or a triaxial braided configuration asillustrated in FIG. 8A. In another embodiment, the first braidedconfiguration of the inner braided thermoplastic comprises a biaxialbraided configuration 114 and the second braided configuration of theouter braided thermoplastic tube 96 b comprises a triaxial braidedconfiguration 117 as illustrated in FIG. 8B. As those of skill willrecognize, alternative first and second braiding configurations may alsobe used.

As shown in FIG. 13, the method 200 further comprises step 210 ofinstalling the overbraided mandrel embedded with at least one loadfitting 100 into a matched tooling assembly 108. For example, FIG. 10Ais an illustration of step 210 of installing the overbraided mandrelembedded with at least one load fitting 100 into the matched toolingassembly 108 which may be used in embodiments of the method 200 (as wellas in method 250 (see FIGS. 14A-B) and method 300 (see FIGS. 15A-B)), ofthe disclosure. The matched tooling assembly 108 preferably comprises ametallic clamshell tooling assembly 110 and at least one load fittinglid 118 made from material, such as steel, stainless steel, or anothersuitable metal.

FIGS. 10B-E illustrate further processing steps of the overbraidedmandrel with embedded load fitting 100 illustrated in FIG. 8. Forexample, and as shown in FIG. 10A, the matched tooling assembly 108preferably comprises a tooling assembly first portion 112. This firstportion 112 comprises a first portion mold side 114 and at least oneload fitting mold side 115 and comprises a second portion 116 having asecond portion mold side (not shown) similar to the first portion moldside 114. The overbraided mandrel 100 may be installed within andbetween the first portion mold side 114 and the second portion moldside, wherein load fitting 103 of the overbraided mandrel 100 isinstalled within the at least one load fitting mold side 115.

Additionally, at least one load fitting member lid 118 may be installedon the load fitting 103 to complete the matched tooling assembly 108. Asshown in FIG. 11, once the matched tooling assembly 108 is closed aroundthe overbraided mandrel embedded with the load fitting 100, the firstportion 112 and the second portion 116 of the matched tooling assembly108 may be held together via a holding element 120, such as a clamp orother suitable device.

Returning to FIG. 13, the method 200 further comprises step 212 ofheating in a heating apparatus 122 the matched tooling assembly 108 withthe installed overbraided mandrel embedded with the load fitting 100. Inone preferred arrangement, heating of the overbraided mandrel 100 takesplace at a specified heating profile in order to consolidate theplurality of inner layers of thermoplastic composite material 96 a andplurality of outer layers of thermoplastic composite material 96 b so asto form a thermoplastic composite tubular structure embedded with atleast one load fitting (see FIG. 8).

FIG. 11 is an illustration of a cut-away perspective view of the matchedtooling assembly 108, such as in the form of the clamshell metallictooling assembly 110, being heated in the heating apparatus 122 that maybe used in the method 200 (as well as in method 250 (see FIGS. 14A-B)and method 300 (see FIGS. 15A-B)) of the disclosure.

As shown in FIG. 11, the heating apparatus 122 comprises a convectionoven 124 comprising heating elements 126. These heating elements emitheat 128 in order to consolidate the plurality of inner layers ofthermoplastic composite material 96 a and the plurality of outer layersof thermoplastic composite material 96 b with at the load fitting 103.The method 200 may allow for fabrication of thermoplastic compositetubular structures embedded with at least one load fitting point in acompletely out of autoclave fabrication method by applying pressureinternally using the expandable material of the mandrel 70. However,although a convection oven 124 is shown in FIG. 11, the heatingapparatus 122 may also consist of an induction oven, an induction heatedmatched tooling assembly, an autoclave, an integrally heated toolingassembly, or another suitable heating apparatus.

Preferably, the specified heating profile comprises a heatingtemperature in a range of from about 150 degrees Fahrenheit to about 800degrees Fahrenheit. More preferably, the heating temperature is in arange of from about 400 degrees Fahrenheit to about 750 degreesFahrenheit. Most preferably, the heating temperature is in a range offrom about 550 degrees Fahrenheit to about 710 degrees Fahrenheit.Preferably, the specified heating profile comprises a heating time in arange of from about 5 minutes to about 120 minutes. More preferably, theheating time is in a range of from about 10 minutes to about 60 minutes.

Upon heating in the heating apparatus 122, the expandable material 72 ofthe mandrel 70 preferably expands and exerts pressure on the pluralityof inner layers of thermoplastic composite material 96 a and pluralityof outer layers of thermoplastic composite material 96 b (see FIGS. 7,8A, and 8B) against the matched tooling assembly 108. This expansioncauses consolidation or hardening of the inner layers of thermoplasticcomposite material 96 a and outer layers of thermoplastic compositematerial 96 b with at least the load fitting 103 so as to form athermoplastic composite tubular structure embedded with the loadfitting, such as the thermoplastic composite tubular structure embeddedwith the load fittings 26 illustrated in FIG. 1.

As used herein, the terms “consolidate” or “consolidation” meanhardening or toughening of the thermoplastic composite material underheat and/or pressure to form a unitary structure, e.g., thermoplasticcomposite tubular structure, and cooling of the hardened or toughenedunitary structure. Heating methods may include induction, microwave,ultrasonic, resistance, hot jet, laser, autoclave, plasma, or anothersuitable heating method, and pressurizing techniques may include mold,contact, fiber tension, roller, vacuum bagging or another suitablepressurizing technique. During consolidation, the heat and/or pressureresults in flow of resin and wetting of reinforcing fibers of thethermoplastic composite material. Preferably, the pressure exerted bythe mandrel 70 on the inner layers of thermoplastic composite material96 a and the outer layers of thermoplastic composite material 96 b maybe in a range of from about 100 psi (pounds per square inch) to about400 psi. In addition, by providing a metallic clamshell tooling assembly110 with smooth, polished surfaces, where pressure is being generatedfrom the inside out, any wrinkles or deformations on the outside of theconsolidated or hardened formed thermoplastic composite tubularstructure embedded with the load fitting may be avoided or minimized.

Returning to FIG. 13, the method 200 further comprises step 214 ofcooling the matched tooling assembly 108 with the formed thermoplasticcomposite tubular structure 26 at a specified cooling profile. Thespecified cooling profile preferably comprises a temperature below aglass transition temperature of the thermoplastic composite material 96a and the thermoplastic composite material 96 b. As shown in FIG. 13,the method 200 further comprises step 266 of removing the formedthermoplastic composite tubular structure from the matched toolingassembly 108. The method 300 illustrated in FIGS. 15A-B includes asimilar process step 316.

As shown in FIG. 13, the method 200 further comprises step 218 ofsolubilizing the mandrel 70 so as to remove the mandrel 70 from theformed thermoplastic composite tubular structure 26. For example, FIG.12 is an illustration of a perspective view of the mandrel 70 beingwashed out of the formed thermoplastic composite tubular structureembedded with at least one load fitting 26 in a mandrel removalapparatus 134 that may be used in the method 200 (as well as in method250 (see FIGS. 14A-B) and method 300 (see FIGS. 15A-B)) of thedisclosure. As shown in FIG. 12, the mandrel removal apparatus 134 maycomprise a washing vessel 136, such as a sink, that dispenses water 138or another water-based solution to wash out and to permanently removethe mandrel 70, such as in the form of the tubular mandrel 78, from theformed thermoplastic composite tubular structure embedded with the loadfitting 26, such as in the form of a thermoplastic composite tube 132.Solubilizing the mandrel 70 thus further comprises solubilizing themandrel 70 with water 138 or a water-based solution to permanentlyremove the mandrel 70 from the formed thermoplastic composite tubularstructure 26. The mandrel 70 may be solubilized and washed out of theformed thermoplastic composite tubular structure 26 in pieces orportions of the soluble, expandable material 72 that forms the mandrel70. The removed mandrel 70 or soluble, expandable material 72 may bediscarded or recycled.

In another arrangement of the disclosure, there is provided athermoplastic composite tubular structure embedded with at least oneload fitting 26 (see FIG. 8) fabricated by the method 200 discussedabove. The thermoplastic composite tubular structure embedded with atleast one load fitting point 26 may comprise a thermoplastic compositetube 132 (see FIG. 8), a pipe, a duct, an elongate hollow structure, oranother suitable thermoplastic composite tubular structure, and may becylindrical or non-cylindrical and may be linear or non-linear.

The description of the different advantageous arrangements has beenpresented for purposes of illustration and description, and is notintended to be exhaustive or limited to the embodiments in the formdisclosed. Many modifications and variations will be apparent to thoseof ordinary skill in the art. Further, different advantageousembodiments may provide different advantages as compared to otheradvantageous embodiments. The embodiment or embodiments selected arechosen and described in order to best explain the principles of theembodiments, the practical application, and to enable others of ordinaryskill in the art to understand the disclosure for various embodimentswith various modifications as are suited to the particular usecontemplated.

The invention claimed is:
 1. A method of manufacturing a thermoplasticcomposite tubular structure embedded with a first load fitting, themethod comprising: braiding a first plurality of inner layers ofthermoplastic composite material around a mandrel, the mandrelcomprising a soluble, expandable material and comprising a mandrelcross-section defining a first closed geometric shape; placing a firstload fitting on the first plurality of inner layers of thermoplasticcomposite material, wherein the first load fitting comprises a main bodyand a clevis that extends from a central portion of the main body, thefirst load fitting treated with an adhesion promoter prior to placingthe loading fitting on the first plurality of inner layers; andoverbraiding a second plurality of outer layers of thermoplasticcomposite material around the main body of the first load fitting andthe mandrel so as to form an overbraided mandrel embedded with the firstload fitting.
 2. The method of claim 1, further comprising the step of:installing the overbraided mandrel embedded with the first load fittinginto a matched tooling assembly.
 3. The method of claim 2, furthercomprising the step of: heating in a heating apparatus the matchedtooling assembly with the overbraided mandrel embedded with the firstload fitting at a specified heating profile in order to consolidate thefirst plurality of inner layers of thermoplastic composite material andthe second plurality of outer layers of thermoplastic composite materialwith the first load fitting so as to form a thermoplastic compositetubular structure embedded with the first load fitting.
 4. The method ofclaim 3, wherein upon heating in the heating apparatus, the expandablematerial of the mandrel expands and exerts pressure on the plurality ofinner and outer layers of thermoplastic composite material against thematched tooling assembly causing consolidation of the plurality of innerand outer layers of thermoplastic composite material with the at leastone fitting.
 5. The method of claim 3, further comprising the steps of:cooling the matched tooling assembly containing the thermoplasticcomposite tubular structure embedded with the first load fitting at aspecified cooling profile, and removing the thermoplastic compositetubular structure embedded with the first load fitting from the matchedtooling assembly.
 6. The method of claim 5, further comprising the stepof solubilizing the mandrel to remove the mandrel from the thermoplasticcomposite tubular structure embedded with the first load fitting.
 7. Themethod of claim 6, wherein, solubilizing the mandrel further comprisessolubilizing the mandrel with water or a water-based solution topermanently remove the mandrel from the thermoplastic composite tubularstructure embedded with the first load fitting.
 8. The method of claim1, wherein, braiding the first plurality of inner layers ofthermoplastic composite material around the mandrel so as to define afirst inner layer depth, and braiding the second plurality of outerlayers of thermoplastic composite material around the first load fittingand the mandrel so as to define a second outer layer depth so as to forman overbraided mandrel embedded with the first load fitting.
 9. Themethod of claim 8, wherein, the first inner layer depth of the firstplurality of inner layers of thermoplastic composite material isdifferent than the second outer layer depth of the second plurality ofouter layers of thermoplastic composite material.
 10. The method ofclaim 1, further comprising the step of: placing a second load fittingon the first plurality of inner layers of thermoplastic compositematerial; and braiding the second plurality of outer layers ofthermoplastic composite material around the first load fitting, thesecond load fitting, and the mandrel so as to form an overbraidedmandrel embedded with the first and second load fitting.